Thousands of Americans die and millions of Americans are injured each year in automobile accidents that involve at least one vehicle traveling with excessive speed. There is no doubt that lives would be saved and fewer accidents would occur if Americans drove at or below the speed limit.
Currently, there are three technologies commonly used to measure the speed of vehicles on the road: radar, manual clocking, and inductive loops. The first two methods are used by safety officers in a proactive mode to enforce the speed limit. The third method is used by traffic flow managers to estimate the speed and to count the number of vehicles on roads throughout the day.
A fourth technology used to measure the speed of vehicles on the road involves passive optical imaging systems. This technology uses cameras to observe the roads and using imaging processing techniques to identify the moving vehicles and estimate their velocities. Analysis techniques that use one camera to estimate the vehicle speed may be broken down into four different categories: (a) single camera to measure vehicle motion across the two-dimensional image, (c) single camera to monitor traffic, to detect vehicle presence, and inaccurately estimate vehicle speed, (c) single camera in-line with vehicle motion to estimate vehicle speed, and (d) single camera with geometry to estimate vehicle speed.
Starting with category (a), analysis techniques in this category identify vehicles in the two-dimensional image and measure the motion across the image. In the image-processing field, this motion across the image is called optical motion, and does not have any relation with the three-dimensional real world. For category (b), the primary purpose of the camera is to monitor the traffic and to detect vehicles on the roadway. Analysis techniques in this category do not present any analytical description of how the vehicle velocity is actually estimated. These details are often left for those ‘skilled in the field’. In category (c), the analysis techniques actually estimate the vehicle velocity, but the camera needs to be placed in-line with the direction of travel of the vehicle. This is often accomplished by placing the camera above the road and the camera points down toward the road observing the vehicle as it passes underneath.
The last category (d) is the most relevant to the present invention. Analysis techniques in this category place the single camera above and to the side of the road being monitored. These analysis techniques often focus on one region of the road usually in the center of the camera's field of view. The geometry used to estimate the vehicle velocity is often dependent on the camera tilt angle and camera pan angle. Since the analysis technique is focused on one region of the road, these analysis techniques may only process one vehicle at a time. Since the analysis technique is optimized for one region, the road must be level in this region for the velocities to be accurate. Also, the vehicles must be traveling in a straight direction.